1. Field of the Invention
The present invention relates to an image forming apparatus, and a method for controlling an image forming apparatus.
2. Description of the Related Art
When a recording sheet passes through a fixing unit of an image forming apparatus, water vapor is generated due to water contained in the recording sheet. In this case, toner (recording agent) on the recording sheet traps the water vapor, thereby generating a phenomenon in which the water vapor blows away non-fixed toner.
This phenomenon is noticeable in a thin line. For example, this phenomenon is called “tailing”, because it seems that a ruled line arranged in the direction parallel to the conveyance direction of the recording sheet leaves trails in spots in the direction perpendicular to the conveyance direction of the recording sheet. The factor causing the tailing will be described below.
Japanese Patent Application Laid-Open No. 2007-206412 discusses a technique for suppressing the generation of density nonuniformity in printing by changing a print speed according to a remaining amount of toner in a cartridge. The technique in Japanese Patent Application Laid-Open No. 2007-206412 pays attention to the relationship between the remaining amount of toner and toner replenishing ability, wherein the print speed is reduced for securing the toner replenishing ability, when the remaining amount of toner becomes a threshold value or less.
Japanese Patent Application Laid-Open No. 2002-244370 discusses a technique in which an edge of image data is detected according to the state of use of a cartridge (information about number of pages, and used amount of toner) for correcting density of the image data in the edge to thereby suppress the generation of a trailing image.
Japanese Patent Application Laid-Open No. 2007-206412 neither pays attention to the relationship between the remaining amount of toner and the generation of a trailing image, nor aims to suppress the generation of the trailing image. Therefore, in Japanese Patent Application Laid-Open No. 2007-206412, the print speed is high when the remaining amount of toner is sufficient. Accordingly, the trailing image is likely to occur (the reason thereof will be described below).
Although the technique in Japanese Patent Application Laid-Open No. 2002-244370 is to suppress the generation of the trailing image, the control thereof is extremely complicated, because the edge in the image data is detected, and then, the density of the image data in the edge is corrected. In Japanese Patent Application Laid-Open No. 2002-244370, since the density of the image data is changed, the density of the image, which is to be actually outputted, is different from the density of the image a user intends.